the control of gene expression Flashcards
Describe substitution
one nucleotide is replaced by another with different base
describe deletion
loss of a nucleotide base from the DNA sequence, causes a frameshift
describe addition
addition of a nucleotide base in a sequence, causes a frameshift
describe duplication
one or more bases repeated, causes a frame shift
Inversion: sequence of bases separated from the DNA sequence and then reattach in the same place but the opposite order
describe translocation
group of bases separated from the DNA sequence on one chromosome and inserted into the DNA sequence on a different chromosome
Explain how the different types of gene mutation result in different amino acid sequences in polypeptides - substitution
the substituted base may produce a stop codon, a codon coding for a different amino acid or a codon coding for the same amino acid
Explain how the different types of gene mutation result in different amino acid sequences in polypeptides - deletion
causes a frameshift. All bases following the substitution shifted to the left causing remaining to codons to be different and potentially code for different amino acids
Explain how the different types of gene mutation result in different amino acid sequences in polypeptides - addition
causes a frameshift. All bases following the substitution shifted to the right causing remaining to codons to be different and potentially code for different amino acids
Explain how the different types of gene mutation result in different amino acid sequences in polypeptides - duplication
causes a frame shift to the right
Explain how the different types of gene mutation result in different amino acid sequences in polypeptides - inversion
amino acid sequence in the area of inversion affected
Explain why some mutations do not result in a changed amino acid sequence
-Different codon coding for the same amino acid may be formed
-this will have no effect on the protein formed.
-This occurs because the genetic code is degenerate
Discuss the causes of gene mutations
-Natural mutation rate (spontaneous mutation) is 1 mutation per 100 000 genes per generation.
-Mutagenic agents increase this rate:
High energy ionising radiation: eg alpha and beta radiation, x rays, UV light.
Chemicals: eg nitrogen dioxide alters DNA structure of interferes with transcription
State what totipotent cells are
Totipotent cells can develop into any types of cell, eg fertilised egg
Explain how cells lose their totipotency and become specialised
-During specialisation only some genes are expressed
-so the cell only makes the proteins it needs to carry out its specialised function.
-A variety of stimuli ensure that the genes that are not needed stay switched off.
Describe cell differentiation and cell specialisation
-Cell differentiation: process by which cells develop into specialised cells.
-No one cell can provide the best conditions for all functions.
-More efficient if they are adapted to their function
Describe the origins and types of stem cells
-Totipotent: in early embryo – develop into any type of cell. Zygote is totipotent. It develops into …
-Pluripotent: in embryos – become almost any type of cell. Eg embryonic and foetal stem cells
-Multipotent: in adults – differentiate into a limited number of specialised cells. Eg bone marrow make blood cells. Eg of -multipotent – adult stem cells, umbilical cord stem cells.
-Unipotent: differentiate into single type of cell – derived from multipotent cells and found in adult tissue”
Explain how pluripotent stem cells can be used to treat human disorders
-Cells can be used to regrow tissues that have been damaged:
Skin grafts for burns. Heart muscle cells for heart damage,
Nerve cells for MS, spinal injury etc Blood cells for leukaemia, Bone cells for osteoporosis, Retina cells for macular degeneration
State what is meant by epigenetics
Heritable changes in gene function due to environmental factors that do not change the base sequence of DNA
Describe the nature of the epigenome
-The epigenome is a series of chemical tags attached to DNA and histones that affects the transcription of DNA
Explain the effect of epigenetic factors on DNA and histones
-The epigenome determines the shape of the DNA-histone complex by changing how tightly wrapped the DNA is.
-When tightly wrapped the DNA cannot be transcribed,
-when loosely coiled DNA can be transcribed
Explain the effects of decreased acetylation of histones
-Gene switched off (inactive):
-Decreased acetylation of histones
-Increased positive charges on histones which increases attraction to phosphate groups on DNA
-Genes tightly packed (condensed)
-Transcriptional factors cannot bind
-Transcription cannot occur so mRNA is not made
-Protein is not produced
Explain the effects of increased methylation of DNA
-Gene switched off (inactive):
-Increased methylation of DNA
-Prevent binding of transcriptional factors to DNA
-Attract proteins that condense DNA/histone complex by inducing deacetylation
-Genes tightly packed (condensed)
-Transcriptional factors cannot bind
-Transcription cannot occur so mRNA is not made
- Protein is not produced
Distinguish between benign and malignant tumours
Benign tumours are not cancerous, malignant tumours are cancerous
Explain the role of oncogenes and tumour suppressor genes in the development of tumours
-Oncogenes: mutations of proto-oncogenes > oncogenes are permanently activated and stimulate cell division causing tumours.
-Tumour suppressor genes: slow cell division> if mutated become inactive > and therefore cell division increases and tumours develop
Explain the effects of abnormal methylation of tumour suppressor genes and oncogenes
-Abnormal methylation of tumour suppressor genes:
-hypermethylation in promotor region of tumour suppressor gene inactivates the gene and transcription is inhibited.
-Tumour suppressor gene no longer reduces cell division
-Abnormal methylation of oncogenes: hypomethylation leads to activation and increased cell division
Explain how increased oestrogen levels can cause breast cancer
-Oestrogen causes transcription factors to become active and increase transcription,
-this can lead to increased cell division
-and therefore tumours if it acts on a gene that controls cell division.
-Oestrogen can also turn proto-oncogenes into oncogenes
Discuss the determination of the genome and proteome of simple organisms
-Relatively easy as prokaryotes contain one circular piece of DNA, no histones, no non coding DNA.
-Can be used to identify proteins that act as antigens on pathogens in order to develop vaccines.
Outline the importance of genome sequencing projects
-Mapping the entire human genome has resulted in identification of single nucleotide polymorphisms (SNPs) that are associated with disease - screening allows early identification and intervention to reduce potential medical problems
-Sequencing prokaryotes and single cell eukaryotes will help cure disease and provide knowledge of genes that can be usefully exploited
Describe the nature of the proteome
The proteome is all of the proteins produced in a given cell/organism, at a given time, under specific conditions
Discuss the determination of the the genome and proteome of complex organisms
-Challenging to translate the genome into a proteome as there are many areas of non coding DNA.
-and as all individuals are different whose DNA should be used to map the genome
